In a video broadcast and/or multicast (hereinafter also referred to collectively as “broadcast/multicast”) application, irrespective of whether over a wireless or a wired network, the recipients of the same video may experience different channel conditions at the same time. Furthermore, the same recipient(s) may also experience different channel conditions at different times. Consequently, the decoded video qualities (either perceptual or in terms of an objective quality measure) for different recipients, or the same recipient at different times, varies.
In accordance with some prior art broadcast/multicast systems, such systems are designed to satisfy a target quality for the user with the worst channel condition (i.e., the highest loss rate). Using this typical approach, users with good channels are unnecessarily penalized.
In one prior art approach, it has been proposed to minimize the maximum performance degradation due to multicast among multiple users. An example of this prior art approach will now be provided, where a single user i with a loss rate pi is considered. Given the total rate constraint Rt, the optimal source coding and channel coding parameters Ai are chosen to minimize the expected end-to-end distortion for this user, with a corresponding minimal distortion Dopti, as follows:
                                          A            i                    =                                                    arg                ⁢                                                                  ⁢                min                                            A                :                                                                            R                      e                                        /                    r                                    <=                  R                                                      ⁢                                                  ⁢                          D              ⁡                              (                                                      p                    i                                    ,                  A                                )                                                    ,                                  ⁢                              D            opt            i                    =                      D            ⁡                          (                                                p                  i                                ,                                  A                  i                                            )                                                          (        1        )            
In the multicast/broadcast case, for a particular source/channel coding scheme characterized by parameter set AM, the end-to-end distortion for user i is DMi(pi,AM). In the prior art approach, it has been proposed to choose AM to minimize the maximum performance degradation among all users. Specifically,
                              A          M                =                              arg                          A              :                                                                    R                    e                                    /                  r                                <=                                  R                  t                                                              ⁢          min          ⁢                      {                                          max                i                            ⁢                              [                                                                            D                      M                      i                                        ⁡                                          (                                                                        p                          i                                                ,                        A                                            )                                                        -                                      D                    opt                    i                                                  ]                                      }                                              (        2        )            
In this way, the receiving quality of each user can be degraded from its optimal performance by a certain amount. However, none of the users are overly penalized.
A problem with the above measure is that it is quite complex to compute. System optimization based on this metric requires intense computation. Moreover, it is also not clear whether equalizing performance degradation due to multicast is an appropriate design criterion.